Alkylation of aromatic hydrocarbons



July 14, 1953` w. A. scHuLzE ALKYLATION OF AROMATIC HYDROCRBONS Filed Aug.l 2, 194s A T TORNEYS Patented July 14, 1953 ALKYLATION oF Anolvnvrnzjv HYnRooARBoNs Walter A. Schulze, Bartlesville, Okla., assignor` to Phillips Petroleum Company,` a` corporation of Delaware Application August 2, 194s, serial No. 42,112

2 Claims. (Cl. 260-671) This invention relates to alkyl aromatic hydrocarbons. In one specific aspect this invention relates to a process for the manufacture of alkyl benzenes of high molecular Weight. In one embodiment, this invention relates to a continuous process for the production of high molecular weight alkyl benzenes Wherein an alkylatable benzene is catalytically alkylated with an olene present as one of the components of a hydrocarbon cracking product initially contaminated with undesirable aromatic hydrocarbons.

'Ihe catalytic alkylation of aromatic hydrocarbons With high molecular Weight polymer olens to produce high molecular weight alkyl benzenes is Well known in the art. Such operations have, in general, been ineflicient'and uneconomical due in part to depolymerization of the polymer, with accompanying losses of olen to the formation of low boiling alkylates.

High molecular weight olens produced by cracking petroleum fractions such as topped crudes, high boiling naphtha, or gas oils, and the like, are unusually stable and serve especially Well as alkylating reactants in the production of high molecular weight alkyl benzenes, and in that respect, are superior to high molecular Weight polymeric olens.

When cracking a petroleum fraction to produce suitable olefin stocks for the alkylation of alkylatable benzenes such as benzene, toluene, Xylene, and the like, to produce high molecular weight alkyl benzenes, high molecular Weight aromatic hydrocarbons boiling in the same range as that of the desired olens, Iare concomitantly formed. I have found that these particular aromatic compounds produce undesirable products When present in a subsequent alkylation step, and therefore they are present as contaminants in the specific cracked product fraction, or olefin stock, ultimately utilized in such an alkylation. When ordinarily alkylating benzene, for example, with such an olen stock contaminated with high boiling aromatic hydrocarbons, a certain portion of the olefin reactants Will alkylate some of the aromatic contaminants to produce undesirable alkylates. When conducting such an -alkylation in the presence of a liquid catalyst, such as, for example, hydrogen fluoride, these contaminating `aromatics also tend to unite With the catalyst to form a complex or a composition which enters the catalyst phase as a catalyst-soluble oil. The alkylatable aromatic hydrocarbon reactant in the alkylation process and the desired high molecular weight alkyl benzene product are dissolved toa considerably high degree in the tov its volume.

catalyst soluble'oil thus formed, adding greatly Such operation is economically undesirable since an unduly large amount of aromatic feed is required, and laborious and expensive recovery operations are-necessary to reclaim the dissolved aromatic feed and alkylate product. Also, catalyst rerun facilities are substantially extended;

This invention has as an object to provide an improved process for the production of high molecular Weight alkyl benzenes.

Another object is to provide a process wherein a product fraction fromA hydrocarbon cracking, which contains desired olefins and undesired aromatic hydrocarbon contaminants, is eiciently utilized as a source 'of high molecular weight olens in an alkylationprocess for the production of high molecular weight alkyl benzenes.

Still another object is `to provide an improved processr for the manufacture of alkyl benzenes especially suitable for the production of surface active agents, detergents, and the like.Y

Other objects and advantages will be appar- Ient, to one skilled in the art, from the accompanying discussion and disclosure.

, I have discovered an improved process for the production of high molecular weight alkyl benvzenes wherein an lalkylatablegbenzene' such as benzene, toluene, xylene, and thelike, is catalytically-alkylated with a highmolecular weight l olefin present asa component in a product fraction from hydrocarbon cracking together with high boilingaromatic hydrocarbons Ias contaminants. The process of my invention is adaptable to the production of alkylates from such olefins 'having not less than 'I or more than 20 carbon atoms per molecule. Suchalkylates have numerous industrial uses, among which is their employment as intermediate in the production of detergents.

The olenstocks employed as alkylating reactants in my process are produced by cracking heavy hydrocarbon fractions, some fractions usually boiling within therange of from 500 to 950 F. The product resulting from cracking such hydrocarbons, Visr fractionated to producea frac- Y tion hereinafter referred to as the crackingproduct fraction, which fraction boils in a range such that it contains olens having at least 7 and not` more than 20 carbon atoms per molecule, preferably 1l to l5carbon atoms. The crackingproduct fraction is usually contaminated with from 5 to 40 Weight per cent high molecular Weight aromatic hydrocarbons, and often contains from l to 50 weight per cent of the desired olens.

My process is carried out in two principal steps, the first of which is a dearomatization of the cracking-product fraction, and the second of which is an alkylation of an -alkylatable benzene with olei'lns in dearomatized cracking-product fraction, to produce a desired high molecular weight alkyl benzene product.

In accordance with my invention, a crackingprcduct fraction of the type above described is contacted in a dearomatization step with a lowboiling olen having not more than 5 carbon atoms per molecule, preferably propylene or ya butylene, in the presence of a relatively weak alkylation catalyst, such as a silica-alumina gel or an acid treated montmorillonite'clay, under such conditions such that the aromatic hydrocarbon contaminants are selectively alkylated with the W-boiling olene and olens, of high molecular weight, produced in the cracking step remain unreacted. I have found that, in order for such a selective alkylation to proceed, it is necessary that the low-boiling olen charged to the dearomatization step be in molar excess over the aromatic hydrocarbon contaminants and that the alkylation be conducted at a temperature within the limits of 300 to 600 F., la pressure suicient to maintain liquid phase, usually within the limits of 200 to 500 p. s. i. g., and at a space velocity within the limits of l to 5 volumes liquid charge per catalyst volume per hour. When operating in this manner, the low-boiling ol'eiins,

kwhich are more reactive than the desired olen reactants, preferentially alkylate the high molecular Weight aromatic hydrocarbon contaminants to produce V.an alkylate boiling at a sufficiently high level, that it can be separated from the desired olens to provide an olen stock, free of aromaticl hydrocarbon contaminants. Such a separation is carried out by ordinary fractionation means. The dearomatized cracking-product fraction is then contacted in an alkylation step with an alkylatable benzene, such as benzene, toluene, xylene or the like, inthe presence of an alkylation catalyst such as liquid hydrogen fluoride, a boron fluoride-hydrogen fluoride complex, a boron fluoride-water complex, or a boron fluoride-aceticacid complex, or the like, under ordinary alkylating conditions, usually a temperature in the range of 80 to 140 F., a pressure sumciently high to maintain the reaction mixture in liquid phase, and at av contact time VWithin the limits of to 80 minutes. Operating in this way, a highly eiiicient alkylation of the alkylatable benzene with the desired olerlns to produce the high molecular alkyl benzene product of the process of this invention is obtained.

My process is especially advantageous in view of the high eiciency with which an alkylatable benzene can be alkylated with a high molecular weight olen present in a cracking product fraction in the type abo-ve described. When operating with my process the loss of valuable olens to the alkylation of the high molecular vweight aromatic hydrocarbon contaminants to produce excessively high boiling alkylates is substantially eliminated. Another advantage offered Aby my process lies in the fact that the formation of excessively large proportions Yof catalystsoluble oils is eliminated, with the consequent substantial `reduction in the loss of desired olens v and alkyl benzene Iproduct to such catalyst solthe remainder,

ing description in which one method of operating my process will be specically disclosed. The figure is a diagrammatic illustration 0f one form of apparatus in which my process may ybe practiced. It is to be understood that this flow diagram is diagrammatic only and may be altered in many respects by those skilled inthe art and remain within the intended scope of my invention.

Referring now to a preferred embodiment of my invention, as illustrated in the ligure, a Mid- Continent crude is fractionated, 'by means not shown, to produce a gas oil boiling in the range of 40G to 700 F. The gas oil thus produced is passed through line I to cracking zone 2 and cracked in the presence of bauxite, at a temperaturein the range of 950 to 1050 F. The eiuent cracking-.product from cracking zone 2 is passed through line 3 to separating means 4 and fractionated to produce a light gasoline fraction withdrawn through line 5, a heavier fraction withdrawn through line 6, a residual fraction withdrawn through line l, and a cracking-product fraction boiling inv the'range of 370 to420 F., withdrawn through line I0. The cracking-product fraction in line I0 contains from 10 to 50 weight per cent of olens having not more than 20 and not less than? carbon atoms per molecule, which are those desired for the alkylation process of my invention. In addition to the olefins, the cracking-product fraction contains from 5 to 40 weight per cent of high molecular weight aromatic hydrocarbons, with paraiiins comprising Such a cracked fraction is passed from line I0, together with fresh propylene from line I3,'and with recycled propylene from line I4, through line I5 to dearomatization zone I6. The mol ratio of propylene to aromatic hydrocarbons in line I5 is greater than 1, and more often within the limits of 1.5:1 to 5:1. In line I5, propylene is present in molar excess over the higher-boiling olens. Material charged to dearomatization zone I6 is passed through a bed of synthetic `silica-alumina catalyst under alkylating conditions such that vthe 'aromatic contaminants are selectively alkylated with propylene to produce isopropyl-aromatic hydrocarbons, which boil abo-ve the range of the desired -olen reactants and such that the desired olens remain substantially completely unreacted. The dearomatization is usually conducted at a temperaturein the range of from 300 to 600 F., a pressure in the range of 200 to 500 p. s. i. g., and at a space velocity within the limits of 1 to 5 volumes total liquid charge per catalyst volume per hour.

Eiiluent from dearomatization zone I6 is passed through line I8 to light o-len recovery zone I9, usually a fractionation step in which unreacted propylene is separated. Propylene is passed from the tcp of zone I9 through line Il and recycled to dearomatization zone I 6. The propylene-free residual product from zone I 9, comprising the unreacted clefins together with isopropyl aromatic hydrocarbons formed in zone I5 and paran hydrocarbons initially present in the cracking-product fraction, is passed from zone I9 through' line 2l to fractionation zone 22 wherein the isopropyl aromatic hydrocarbons are separated as residual product, which is passed from zone 22 through lines 24'and 20, in -part or in Whole as `desired forutilization elsewhere, or in any desired proportionthrough lines 30 and 53 for further fractionation with the `product of a subsequent alkylation step.

The overhead product of fractionation zone 22 is an aromatic-free fraction containing the desired olens together With some parains, and is passed from zone 22 through line 23 to alkylation zone 28. Benzene, including fresh benzene from line 3|, and recycled benzene from line 32, discussed more fully hereinafter is passed through line 29 to alkylation zone 28 simultaneously with the olefin stock in line'23. If desired, the charge material in lines 29 and 23 may lbe admixed and the -ad'mixture charged to zone 28. In any event, the overall mol ratio, i. e., the external mol ratio ofV olen to benzene about'to enter zone 28 is between 1:3 and 1:15, preferably in the range of 1:4 to 1:10. Alkylation Zone 28 contains liquid hydrogen fluoride in a. volume ratio to hydrocarbon within the limits of 1:1 to 1:5, preferably from 1:2 to 1:4.

The reaction mixture in alkylation zone 28 is thoroughly agitated by suitable stirring means 34, to effect uniform reaction and to maintain the ordinarily immiscible catalyst and hydrocarbon layers in one continuous phase. Ordinary alkylating conditio-ns are usually maintained in alkylation zone 28. Under such con- -ditions the reaction is maintained at a temperature in the range of from 80 to 140 F., a pres,- sure sufficient to maintain the reactants in liqf uid phase and a contact time within the limits of 15 to 80 minutes, more preferably 20 to 60 minutes. Since the density -of the liquid hydrogen fluoride catalyst is quite high, a continuously circulating stream is drawn at the bottom of alkylation zone 28 through line 36, and recirculated by pump means (not shown) to zone 28 through line 33.

Effluent from alkylation zone 28 is passed through line 38 to separation zone 39 wherein a liquid hydrocarbon-rich phase and a relatively heavy hydrogen fluoride-rich catalyst phase are separated. The heavier catalyst phase, i. e., the hydrogen fluoride-rich phase in separation zone 39, may be recycled directly to alkylation zone 28 through lines 40, 4| and 33. However, the catalyst phase is contaminated with Water and other impurities and it is therefore desirable to pass at least a portion of it through lines 40 and 42 to a purification or catalyst rerun unit 44. One of the impurities besides water, which is removed from the catalyst phase in the acid rerun unit, is the .so-called catalyst-soluble oils. The catalyst-soluble oils, a Icy-product of the alkylation reaction, vary considerably in composition but are, in general, normally liquid materials and are soluble in hydrogen fluoride. The presence yof catalyst-soluble oils as impurities, reduces the catalytic activity of the hydrogen-4 fluoride catalyst and must necessarily be removed, in a major proportion, as required for maintaining the desired catalyst activity. The amount of catalyst-soluble oils usually present in the catalyst phase varies from about 1-2 per cent by weight to as high as about per cent by Weight. Other impurities in the catalyst phase are minor amounts of physically Ldissolved hydrocarbon reactants and product. In Vcatalyst rerun unit M, usually a fractionation system, water and other impurities are withdrawn through lines 59 and 55. A purified catalyst phase is passed from catalyst rerun unit 44, through line -45 and recycled through line 33 to alkylation zone 28.

The lighter hydrocarbon-rich phase contains an amount of dissolved hydrogen fluoride, usually within the limits of l to 3 per cent and is passed from separation zone 39 through line 49 to fractionation zone 5|, where unconverted benzene together with hydrogen fluoride is separated, and recycled from the top of zone 5| through lines 32 and 29 to alkylation zone 28. In some instances, it may be preferable to separate the dissolved hydrogen fluoride from the hydrocarbon phase, prior to its introduction to zone 5|, by fractionation means not shown.

Benzene-free, hydrogen fluoride-free, bottom product of fractionation Zone 5| contains, primarily, the desired alkylate product along with minor amounts of by-product heavy alkylate formed in zone 28, and some parans, and is passed through lines 52 and 53 to fractionation zone 54 along with bottom product from fractionation zone 22 passing into line 53 from line 39.

Parains along with small concentrations of any polymer by-product, formed from low-boiling olens in zone I6, are separated as an overhead product in fractionation zone 5d, and are passed from the top of fractionation zone 54 through line 56 for utilization elsewhere. Bottom product from fractionation zone 54 is passed through line 5l to fractionation zone 58, usually operated at atmospheric pressure or lower. In fractionation zone 58, the high molecular weight alkyl benzenes formed by the alkylation of benzene with the desired olefin in the cracking product fraction, described hereinabove, are separated as an overhead product and removed as products of the process through line 59. Bottom product boiling above the boiling range of the desired alkylate product of my process, is discharged through line 6| The higher boiling bottom product passing through line 38 from fractionation zone 22, comprises isopropyl aromatics, at least a portion of which may boil in the desired alkylate range. The portion of the materials in line 59, boiling in the range of the alkylate product is discharged through line 59, with the product from fractionation. zone 58, and contributes to the yield. The portion of materials from line 30, boiling above the alkylate range is discharged from fractionation zone 58, as bottom product, through line 6|. In some instances, minor amounts of low-boiling olen, such as from 2-5 per cent, are converted to polymers in the dearomatization step. Such polymers when boiling in the same range as the cracking product fraction, are carried into the alkylation step (zone 28), and alkylate the benzene, a portion of the resulting alkylate which is added to the product, while the remainder is removed overhead from fractionation zone 54. While the amount of low-boiling alkylate from the dearomatization step is usually small, its addition to the overhead product in line 56 contributes a certain degree of armoaticity which enhances the value of the overhead material in line 56 for solvent purposes. Should any minor amount of unsaturates from this source be objectionable, the entire stream or any portion thereof, may be discharged from the system through line 28.

The catalysts used in the dearomatization step of my process are of such nature that alkylation of the more reactive low-boiling hydrocarbons with the aromatic contaminants proceeds freely, while the desired olefin reactants of the cracking product fraction remain substantially unreacted. Catalysts most often used in the dearornatization step 'are solid catalysts such as silica-alumina, acid-treated montmorillonite and the like. Among thevarious catalysts that can be used in the dearomatization step, I prefer silica-alumina catalysts, preferably those containing per cent or less by weight, of alumina. My preferred dearomatization catalysts are most accurately described as synthetic silica-alumina gels of Such a nature that it is possible to choose conditions for my process which provide excellent selectivity toward alkylation Iwithout incurring extensive clen polymerization.

My preferred silica-alumina catalysts are prepared by first forming a hydrous gel or jelly, from an alkali-silicate, such as sodium silicate, and an excess of an acid, such as hydrochloric acid; washing soluble material from the gel; treating or activating the gel with an aqueous solution of an aluminum salt, such as aluminum sulfate, and subsequently Washing and drying the treated material. In this manner, a part of the aluminum, presumably in the form of a hydrous oxide or loose hydroxide compound, formed by hydrolysis, is selectively absorbed by the hydrous silica, and is not removed by subsequent washing, which serves to remove unabsorbed salts and free acid. The washed gel is then dried at moderate temperatures, which produces hard brittle granules of gel containing negligible quantities of compounds` other than silica and the absorbed alumina.

The catalysts most often used in the alkylation step of my process are well known liquid alkylation catalysts, such as liquid hydrogen fluoride, liquid hydrogen fluoride-boron uoride com plexes, and complexes of boron fluoride formed with compounds such as water, acetic acid, diethyl ether, ethanol and the like. Among the various `catalysts that can be used in the alkylation step, I prefer to use liquid hydrogen fluoride which is commercially available, and an especially eicient alkylation catalyst for the alkylation step of my process.

Advantages of this invention are illustrated by the following example. The reactants, and their proportions, and other specic ingredients are presented as being typical and should not be construed to limit the invention unduly.

A gas oil fraction cut from a Mid-Continent Crude, and boiling in the range of 50G-'700 F., was cracked in the presenceof bauxite at a temperature within the range of 950 F. to 1050 F. The total product was fractionated to produce a cracking-product fraction boiling in the range of S80-460 F., which contained 18 weight per cent olens and 3'? weight per cent aromatic hydrocarbons. The cracking-product fraction was admixed with propylene under suficient pressure to provide an admixture containing propylene in molar excess over higher oleiins, and in a mol ratio to the aromatic hydrocarbon of 3:1. The admixture was passed through a bed of silica-alumina catalyst in a dearomatization step, at a temperature of 400 F., at a pressure of 300 p. s. i. g., and at a space velocity of 1.8 liquid volumes charge per catalyst volume per hour. In the silica-alumina catalyst zone, isopropyl aromatic hydrocarbons 4were formed, and the desired olens, i. e., those present in the cracking product fraction, were substantially unreacted. Eiuent from the silicaalumina catalyst Zone was stripped of unreacted propylene and fractionated to separate the desired olefin, along with some accompanying parafns, from the relatively heavy isopropyl aromatic alkylate. The aromatics-free oleiin-containing `fraction was charged to an alkylation zone in admixture with benzene. The mol ratio of benzene to olefin in the admixture at the alkylation inlet was 8: 1. Liquid hydrogen fluoride was present in the alkylation zone in an amount to comprise 48 volume per cent of the total reaction mixture. The reaction mixture was agitated by stirring at F., the fiow rate of the reactants being regulated to provide a contact time of 66 minutes. The alkylation reactor efuent was separated by gravity into a liquid hydrocarbon-rich phase, and a relatively heavy liquid catalyst phase. The catalyst phase was recycled to the reactor and the hydrocarbon phase passed to a fractionation system. In a rst fractionation step, unreacted benzene was separated from the hydrocarbon phase for recycle to the alkylation reactor. In a second fractionation step, paraiiin hydrocarbons previously associated lwith the olens in the cracking product fraction, were separated within an overhead temperature range of from BOO-500 F. The resulting total alkylate was fractionated in a nal fractionation step at atmospheric pressure, to separate the undesirable and relatively small amount of heavy by--product alkylate from the desired alkylate product. The desired alkylate product was obtained as an overhead product Within a temperature range of 525-680 F.

The process above described was repeated eX- cept that the dearomatization step Was omitted. The crackingproduct fraction was charged together with benzene directly to the alkylation step. In the latter instance about 30 per cent of the alkylate product was dissolved in the catalyst-soluble oils formed during the alkylation, and additional fractionation steps were required for recovery of the product.

The yield of vdesired alkylate was higher, and formation of undesirable heavy yproduct and of catalyst-soluble oils Was less, when rst removing the aromatic hydrocarbon contaminants from the cracking product fraction. These results are exemplied in the following tabulation.

. Without Yield Ygg'rg' Dcaromutization Desired alkylate 1 l. 080 l. 033 By-product alkylate 1 0.190 0. 301 Catalyst-soluble oil l. n 0. 301 0. 837

1 Lb./lb. olefin.

As will be evident to those skilled in the art, various modifications can be made or followed in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims. i

I claim:

1. A process for the manufacture of a high molecular weight alkyl benzene, comprising cracking a petroleum fraction having a boiling range above 400 F., recovering from the product of said cracking a fraction containing aromatic hydrocarbons in an amount Within the limits of 5 to 40 per cent by weight and olens in an amount within the limits of 10 to 50 per cent by Weight and boiling in a range such that said olefins have not more than 20 and not less than 'l carbon atoms per molecule; admixing the cracking-product fraction, above described, With a low-boiling olen having not more than 5 carbon atoms yper molecule in an amount in molar excess over said olens having from 7 to 20 carbon atoms per molecule and in a mol ratio to said aromatic hydrocarbons within the limits of 1.5:1 to 5:1, contacting the resulting admixture with 'a synthetic silica-alumina catalyst containing alumina in an amount not greater than 10 per cent and prepared by treating a hydrous silica gel with an aqueous solution of an aluminum salt to absorb not more than per cent alumina on said silica and subsequently Washing and drying the resulting silica-alumina gel, effecting said contacting at a temperature in the range of 200 to 500 p. s. i. g., and at a space velocity of from 1 to 5 volumes total liquid charge per catalyst volume per hour, whereby said aromatic hydrocarbons are alkylated with said 10W-boiling olen and higher boiling olens in said crackingproduct fraction are substantially unreacted; recovering unreacted low-boiling olen hydrocarbon from the reaction mixture and recycling same to the zone of said contacting; separating the thus formed alkylate from the reaction mixture thereby providing a cracking product substantially free of aromatic hydrocarbons and containing olens having not more than 20 and not less than 7 carbon atoms per molecule; contacting the aromatics free fraction with an alkylatable benzene in the presence of a catalyst comprising liquid hydrogen fluoride at a temperature Within the limits of 80 to 140" F., a pressure sufficient to maintain the reaction mixture in the liquid phase, for a duration within the limits of to 80 minutes at an overall mol ratio of olefin to said alkylatable benzene Within the limits of 1:4 to 1:10 and at a catalyst to hydrocarbon Volume ratio within the limits of 1:1 to 1 :5, separating total eiiluent from said contacting in the presence of liquid hydrogen uoride into a liquid hydrocarbon-rich phase and a liquid hydrogen fluoride-rich phase, recycling at least a portion of said hydrogen fluoride phase to the zone containing said hydrogen fluoride catalyst', separating unreacted alkylatable benzene from said hydrocarbon phase and recycling said benzene to said zone containing hydrogen fluoride, separating parains boiling below about 500 F. from the hydrocarbon phase thus free of said alkylatable benzene, and recovering from the remaining hydrocarbon phase a high molecular weight alkyl benzene boiling in the range of 500 to '700 F. as a product of the process.

2. A process in accordance with claim l Wherein said alkylatable benzene is benzene and said 10W-boiling olen is propylene.

WALTER A; SCHULZE.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,994,249 Ipatiei et al Mar. 12, 1935 2,001,907 Ipatieff May 21, 1935 2,260,279 dOuville et al Oct. 21, 1941 V2,343,870 Kaplan Mar. 14, 1944 2,404,340 Zimmerman July 16, 1946 2,410,111 Thomas Oct. 29, 1946 2,413,161 Zerner et al Dec. 24, 1946 2,437,356 Hill Mar. 9, 1948 2,439,457 Donleavy et al Apr. 13, 1948 2,456,119 Friedman et al Dec. 14, 1948 OTHER REFERENCES Alfred W. Francis, Chemical Reviews, Vol. 43, page 258. 

1. A PROCESS FOR THE MANUFACTURE OF A HIGH MOLECULAR WEIGHT ALKYL BENZENE, COMPRISING CRACKING A PETROLEUM FRACTION HAVING A BOILING RANGE ABOVE 400* F., RECOVERING FROM THE PRODUCT OF SAID CRACKING A FRACTION CONTAINING A AROMATIC HYDROCARBONS IN AN AMOUNT WITHIN THE LIMITS OF 5 TO 40 PER CENT BY WEIGHT AND OLEFINS IN AN AMOUNT WITHIN THE LIMITS OF 10 TO 50 PER CENT BY WEIGHT AND BOILING IN A RANGE SUCH THAT SAID OLEFINS HAVE NOT MORE THAN 20 AND NOT LESS THAN 7 CARBON ATOMS PER MOLECULE; ADMIXING THE CRACKING-PRODUCT FRACTION, ABOVE DESCRIBED, WITH A LOW-BOILING OLEFIN HAVING NOT MORE THAN 5 CARBON ATOMS PER MOLECULE IN AN AMOUNT IN MOLAR EXCESS OVER SAID OLEFINS HAVING FROM 7 TO 20 CARBON ATOMS PER MOLECULE AND IN A MOL RATIO TO SAID AROMATIC HYDROCARBONS WITHIN THE LIMITS OFF 1.5:1 TO 5:1, CONTACTING THE RESULTING ADMIXTURE WITH A SYNTHETIC SILICA-ALUMINA CATALYST CONTAINING ALUMINA IN AN AMOUNT NOT GREATER THAN 10 PER CENT AND PREPARED BY TREATING A HYDROUS SILICA GEL WITH AN AQUEOUS SOLUTION OF AN ALUMINUM SALT TO ABSORB NOT MORE THAN 10 PER CENT ALUMINA ON SAID SILICA AND SUBSEQUENTLY WASHING AND DRYING THE RESULTING SILICA-ALUMINA GEL, EFFECTING SAID CONTACTING AT A TEMPERATURE IN THE RANGE OF 200 TO 500 P. S. I. G., AND AT A SPACE VELOCITY OF FROM 1 TO 5 VOLUMES TOTAL LIQUID CHARGER PER CATALYST VOLUME PER HOUR, WHEREBY SAID AROMATIC HYDROCARBONS ARE ALKYLATED WITH SAID LOW-BOILING OLEFIN AND HIGHER BOILING OLEFINS IN SAID CRACKINGPRODUCT FRACTION ARE SUBSTANTIALLY UNREACTED; RECOVERING UNREACTED LOW-BOILING OLEFIN HYDROCARBON FROM THE REACTION MIXTURE AND RECYCLING SAME TO THE ZONE OF SAID CONTACTING; SEPARATING THE THUS FORMED ALKYLATE FROM THE REACTION MIXTURE THEREBY PROVIDING A CRACKING PRODUCT SUBSTANTIALLY FREE OF AROMATIC HYDROCARBONS AND CONTAINING OLEFINS HAVING NOT MORE THAN 20 AND NOT LESS THAN 7 CARBON ATOMS PER MOLECULE; CONTACTING THE AROMATICS FREE FRACTION WITH AN ALKYLATABLE BENZENE IN THE PRESENCE OF A CATALYST COMPRISING LIQUID HYDROGEN FLUORIDE AT A TEMPERATURE WITHIN THE LIMITS OF 80 TO 140* F., A PRESSURE SUFFICIENT TO MAINTAIN THE REACTION MIXTURE IN THE LIQUID PHASE, FOR A DURATION WITHIN THE LIMITS OF 15 TO 80 MINUTES AT AN OVERALL MOL RATIO OF OLEFIN TO SAID ALKYLATABLE BENZENE WITHIN THE LIMITS OF 1:4 TO 1:10 AND AT A CATALYST TO HYDROCARBON VOLUME RATIO WITHIN THE LIMITS OF 1:1 TO 1:5, SEPARATING TOTAL EFFLUENT FROM SAID CONTACTING IN THE PRESENCE OF LIQUID HYDROGEN FLUORIDE INTO A LIQUID HYDROCARBON-RICH PHASE AND A LIQUID HYDROGEN FLUORIDE-RICH PHASE, RECYCLING AT LEAST A PORTION OF SAID HYDROGEN FLUORIDE PHASE TO THE ZONE CONTAINING SAID HYDROGEN FLUORIDE CATALYST, SEPARATING UNREACTED ALKYLATABLE BENZENE FROM SAID HYDROCARBON PHASE AND RECYCLING SAID BENZENE TO SAID ZONE CONTAINING HYDROGEN FLUORIDE, SEPARATING PARAFFINS BOILING BELOW ABOUT 500* F. FROM THE HYDROCARBON PHASE THUS FREE OF SAID ALKYLATABLE BENZENE, AND RECOVERING FROM THE REMAINING HYDROCARBON PHASE A HIGH MOLECULAR WEIGHT ALKYL BENZENE BOILING IN THE RANGE OF 500 TO 700* F. AS A PRODUCT OF THE PROCESS. 